Angel Island State Park Weather

Angel Island sits in the middle of San Francisco Bay at an elevation of 788 feet at Mt. Livermore, which puts it in an unusual meteorological position: high enough to poke above the marine layer on foggy days, but surrounded by water on all sides, which keeps temperatures mild year-round. Average highs run from about 57°F in winter to 73°F in September, with lows hovering between 46°F and 57°F depending on the season. The island averages 9.6 hours of sunshine per day and earns a comfort score of 79 out of 100, which is genuinely good for the Bay Area. Morning fog is common but typically clears within a couple of hours. Wind is real here, especially on the ridge and exposed western slopes, so even a warm-looking forecast can feel cooler than expected once you get up high. The overall climate is cool, breezy, and sunny more days than not, with a distinct wet season from November through February and virtually no rain from May through August.

September is the best single month to visit Angel Island. Highs reach 73°F, the fog drops to just 0.8 hours per day (the lowest of any month in the dataset), there is almost no rain, and the comfort score hits 85 out of 100. The light in September is warm and golden, the crowds thin out after Labor Day, and the bay views are as clear as they get all year. April is a strong second choice, with highs around 66°F, a comfort score of 84, minimal rain, and the hills still green from winter. July is also excellent at 85 comfort with 11 hours of sunshine and zero precipitation, though it comes with slightly more morning fog than September. The worst months are November and December, when rain totals climb to 8 inches and comfort scores dip into the 60s. If you can only pick one window, the stretch from late September through October (before the rains arrive) and the April-to-September summer corridor are both excellent. See best months for hiking in the Bay Area for a broader seasonal comparison.

Yes, and it is one of the most distinctive things about the island. The marine layer that rolls in from the Pacific typically sits between 500 and 1,500 feet in elevation during summer months. At 788 feet, Mt. Livermore's summit can sit right at the fog ceiling or above it, giving you unobstructed sunshine and views while Sausalito and the Marina District below are wrapped in gray. It does not happen every foggy day, since deep marine layers can push well above 788 feet. But on typical summer mornings when the fog is shallow and burning off by midday, the ridge trail on Angel Island is one of the better places in the Bay to be above it all. The key indicator is fog height: if you can see the island's peak from shore, it is above the layer. Morning fog on Angel Island averages just 2 hours per day in summer, and only 0.8 hours in September, suggesting the elevation advantage is real and consistent. Read more about how elevation affects fog in the Bay Area.

Angel Island can be quite windy, particularly on the western and northern slopes that face directly into the prevailing westerly and northwesterly flow that pushes through the Golden Gate corridor. The ridge at Mt. Livermore is the most exposed point, and wind speeds there regularly exceed what you would feel at sea level in nearby towns. The Bay Area's afternoon wind pattern intensifies from late spring through summer as inland heat pulls cool ocean air eastward through gaps in the Coast Range. Angel Island sits right in this flow path. Summer afternoons are windiest, with gusts that can make a 70°F day feel significantly cooler. Morning hours are calmer, and the eastern slopes of the island provide more shelter from the prevailing wind direction. This wind pattern is a consistent feature of Bay Area geography, not unusual weather. For context on why the region is so persistently breezy, why the Bay Area has so much wind explains the mechanics well. Come prepared regardless of season: the ridge will almost always be windier than the forecast suggests.

The ferry crossing from Tiburon or San Francisco can feel dramatically different depending on the season and time of day. In summer, morning departures often cross through or beneath the marine layer while it is still low over the bay, which means cool, damp air, reduced visibility, and a noticeable drop in temperature on the water. The wind on the bay adds a significant chill factor even when the thermometer reads mild temperatures. By midday most summer days, the fog has either lifted or pulled back toward the coast, and the crossing becomes sunny and pleasant. Fall and spring crossings are generally clearer, with better visibility and calmer conditions. Winter crossings can be rainy and choppy when storm systems move through. The bay is always cooler and windier than land, so even on a mild day in the 60s, the boat deck can feel like the 50s once you factor in wind chill. Bay Area sea breezes explains why conditions on the water diverge so much from what land-based forecasts show.

Layers are non-negotiable. The standard Bay Area approach applies here in an amplified form because you are combining island exposure, bay wind, and elevation gain all in one trip. Start with a moisture-wicking base layer, add a mid-layer fleece or light insulating jacket, and bring a windproof outer shell even if the forecast looks warm. On summer days when the city is in the low 60s, the ridge at Mt. Livermore can feel like the low 50s once the afternoon wind picks up. On September days when the bay area feels genuinely warm, you may not need more than a light jacket at the summit. Sunscreen matters more than most people expect, since you can be hiking in full sun at elevation with a cool breeze that masks how much UV you are absorbing. Bring more water than you think you need: the ferry does not make return trips every few minutes, and the trails are exposed. A hat with a brim handles both sun and wind. Dressing in layers for San Francisco weather lays out the logic for the whole region, and it applies directly here.

Angel Island follows the Bay Area's classic Mediterranean rain pattern: essentially dry from May through September, then progressively wetter from October through February, with spring months tapering back to dry. June, July, and August each record zero inches of precipitation. The rain arrives in earnest in October, builds through November (around 8 inches) and December (1 to 4 inches), and January adds another 7 inches on average. February starts the retreat with about 4 inches, and by March the total is down to half an inch. April and May each see minimal rainfall. The wet season on Angel Island is not dramatically different from nearby Tiburon or Marin Headlands, since the island sits in the bay rather than on the windward coast. Winter hiking on Angel Island is absolutely possible during dry spells, and the trails and views on a clear January or February day can be stunning, but you should always check the forecast before going. Wet trails on exposed slopes can be slippery, and a winter storm on the bay is a genuinely cold, miserable experience. For the broader regional rain picture, the rainiest month in the Bay Area has useful context.

On a typical summer day, the marine layer that settles over the bay overnight and in the early morning hours begins clearing somewhere between 10 AM and noon, though this varies considerably by month and year. Angel Island averages 2.0 hours of fog per day across the year, with the foggiest month being May at 2.5 hours and the clearest being September at just 0.8 hours per day. June, July, and August each average around 1.8 to 2.2 hours of fog, which is almost always concentrated in the morning. The clearing process is driven by solar heating: as the sun warms the land, the temperature inversion that holds the fog layer in place weakens, and the marine layer retreats westward toward the coast. On Angel Island specifically, the elevation advantage at Mt. Livermore means the summit often clears before the lower shoreline does. If you are arriving on a morning ferry, expect fog or low overcast on the bay and in the lower parts of the island, with a reasonable chance of clearing by the time you complete a ridge loop. Why morning fog forms in the Bay Area explains the daily fog cycle in detail.

September and October consistently deliver the best long-distance visibility from Angel Island's ridgeline. September has the lowest fog average of any month (0.8 hours per day), warm afternoons, and the atmospheric clarity that comes after the long dry summer. On clear September and October days, you can see from the Farallon Islands 27 miles offshore all the way east to Mount Diablo. April is also excellent for visibility, especially after a late-winter rain system scrubs the atmosphere clean. The worst visibility months are not necessarily the foggiest but the rainiest: November and December bring overcast, low cloud ceilings, and occasional rain that cuts views down to a few miles or less. Summer fog is more predictable and usually clears by midday, while winter overcast can persist all day. For comparison, Alcatraz Island sits at a much lower elevation and gets socked in far more reliably in summer than Angel Island does. The 788-foot elevation at Mt. Livermore is a significant advantage for views on days when the marine layer is shallow.

Angel Island is an excellent summer hiking destination, with the main caveat being wind on the exposed ridge. Temperatures in June, July, and August hold steady in the high 60s to low 70s, with comfort scores of 84 to 86 out of 100, zero rainfall, and 10 to 12 hours of sunshine per day. The Perimeter Road and the ridge trail up to Mt. Livermore are largely unshaded, which means full sun exposure for much of the hike. This is actually a plus in the Bay Area where cool marine air keeps temperatures in a comfortable range even in full sun, but it makes sunscreen and a hat essential rather than optional. The western slopes face the afternoon wind directly, so the ridge section can be bracing even on a warm afternoon. The eastern and southeastern slopes near Ayala Cove are noticeably more sheltered and warmer. Morning hikes in summer start cool and often foggy, then open up to full sun as the marine layer retreats. The combination of mild temperatures, long daylight, and reliable sunshine makes summer the peak season for hiking here, with September adding the bonus of lower fog and exceptional clarity. The Bay Area's four seasons covers how summer hiking conditions differ from the rest of the year across the region.